linux-kernel - Re: [PATCH 1/1] mm: memcontrol: fix vmstats_percpu state incorrect subtraction after reparent

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Date:   Mon, 27 Mar 2023 09:29:37 +0800
From:   Cai Xinchen <caixinchen1@...wei.com>
To:     <mkoutny@...e.com>
CC:     <songmuchun@...edance.com>, <akpm@...ux-foundation.org>,
        <hannes@...xchg.org>, <longman@...hat.com>, <mhocko@...nel.org>,
        <roman.gushchin@...ux.dev>, <shakeelb@...gle.com>,
        <cgroups@...r.kernel.org>, <duanxiongchun@...edance.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <yosryahmed@...gle.com>, <mpenttil@...hat.com>
Subject: Re: [PATCH 1/1] mm: memcontrol: fix vmstats_percpu state incorrect
 subtraction after reparent

Yes, only cgroup v1.

On 2023/3/25 1:11, Michal Koutný wrote:
> Hello.
>
> On Mon, Mar 20, 2023 at 03:06:48AM +0000, Cai Xinchen <caixinchen1@...wei.com> wrote:
>> When memcg C is offllined, its pages are reparented to memcg P,
>> so far P->vmstats (hierarchical) have those pages, and
>> P->vmstats_percpu (non-hierarchical) don't. When those pages get
>> uncharged, P->vmstats (hierachical) decreases, which is correct,
>> but P->vmstats_percpu (non-hierarchical) also decreases, which
>> is wrong, as those stats were never added to P->vmstats_percpu to
>> begin with.
> I was wondering why ->vmstats_percpu matters (in the end all is summed
> in ->vmstats) -- do you mean this is a cgroup v1 only issue? As only
> that exposes the non-hieararchical stats.
>
> Thanks,
> Michal